System and method for multipath processing of image signals

ABSTRACT

The invention generally relates to intravascular imaging system and particularly to processing in multimodal systems. The invention provides an imaging system that splits incoming image data into two signals and performs the same processing step on each of the split signals. The system can then send the two signals down two processing pathways. Methods include receiving an analog image signal, transmitting the received signal to a processing system, splitting the signal to produce a first image signal and a second image signal, and performing a processing operation on the first image signal and the second image signal. The first and second signal include substantially the same information as one another.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of, and priority to, U.S.Provisional Application Ser. No. 61/745,388, filed Dec. 21, 2012, thecontents of which are incorporated by reference.

FIELD OF THE INVENTION

The invention generally relates to intravascular imaging system andparticularly to processing in multimodal systems.

BACKGROUND

Ultrasound imaging is used in medicine to examine tissue with soundsignals at a frequency higher than the normal range of human hearing. Toillustrate, engine noise from a typical truck might include 125 Hzsounds while birds may chirp at about 6,000 Hz. A typical intravascularultrasound device might operate at 40,000,000 Hz (i.e., 40 MHz).

In medical ultrasound, a probe device sends sound waves through tissue.The sound waves bounce off features in the tissue and back to thetransducer. The transducer converts the waves to an electrical signaland sends it to an image processing system. Typically, the imageprocessing system converts the electrical signal to a digital signal,which can then be displayed on a computer monitor (allowing a doctor tosee the patient's blood vessels) or stored for other analyses.

In fact, looking at the tissue is but one use of IVUS. Some IVUS systemsare used to perform “virtual histology”, which involves analyzing anultrasound signal to classify features in a patient's tissue (e.g.,plaque, dead tissue, healthy tissue). IVUS can also be used to study theflow of blood within a patient. The velocity at which blood is flowingwill typically produce a characteristic Doppler signature. Thisinformation can help identify is a patient is suffering from restrictedblood flow due to, for example, atherosclerosis, or plaques.

The very fact that an IVUS signal may be put to more than one use isassociated with challenges in the design and maintenance of IVUSsystems. Any change in the signal processing that benefits one intendeduse can cause problems in another end-use. For example, in someultrasound systems, transient resonances from the transducer producesignals, called ringdown, that detract from a visual display. Aprocessing step can be added to the system that removes the ringdownfrom the signal. However, the ringdown signal does provide some dataabout the tissue that is useful in virtual histology. Thus, if thesystem is also used for virtual histology, yet another step must beadded that puts the ringdown data back into the signal for the virtualhistology application.

U.S. Patent Publication 2011/0087104 to Moore describes a system that“splits” the signal for imaging and for parametric (e.g., virtualhistology) analysis. However, such a system requires duplicate, parallelhardware components that operate in tandem in the different signalprocessing pathways. Not only does duplicate internal hardware requireadditional design and manufacturing costs, it also raises somesignificant difficulties in subsequent modifications of the systems toadd other image analysis tools.

SUMMARY

The invention provides an imaging system that splits incoming image datainto two signals and performs the same processing step on each of thesplit signals.

The system can then send the two signals down two processing pathways.Where one of the pathways is used to provide medical information, asubsequent change or addition to the other pathway does not affect thefirst pathway. For example, if one pathway provides a grayscale imageand the other is used in virtual histology, the addition of a processingstep such as ringdown subtraction in the grayscale pathway requiresneither a compensating step in the virtual histology pathway noradditional hardware to be added. The system is flexible because futurechanges, included unforeseen changes, can be accommodated withoutcomplex measures. The flexibility of the system lowers lifetimeoperating costs of medical imaging operations due to the fact that newmodalities can be implemented without new processing hardware orengineering efforts. Lower operating costs allows use of the medicalimaging system to reach a greater number of patients, improving agreater number of lives.

In certain aspects, the invention provides a method of imaging tissuethat includes receiving an analog image signal from an ultrasonictransducer, transmitting the received signal to a processing system,splitting the signal to produce a first image signal and a second imagesignal, and performing a processing operation on the first image signaland the second image signal. The first and second signal includesubstantially the same information as one another. For example, an imagesignal can be split and then each copy can be amplified as a method oftime gain compensation. The two TGC amplified signals can then bedigitized in parallel. Alternatively, the analog signal can be digitizedprior to (e.g., just prior to) splitting. The processing that isperformed on both signals can be performed within the same processor.For example, a field-programmable gate array can be deployed with aredundant logic that does the same thing in parallel to each signal.Alternatively or additionally, the processor could include anapplication specific integrated circuit, a general purposemicroprocessor, or other hardware. A signal can also be processed byhardware such as an amplifier or filter. In some embodiments, methods ofthe invention include deriving different types of images or signals(e.g., 2D displays and virtual histology analyses) from the first andsecond signal, i.e., the first type of image comprises a grayscale imageand the second type of signal comprises a tissue characterization.

In related aspects, the invention provides an intravascular ultrasoundimaging system that includes an elongated catheter with a transducer ata distal portion of the catheter and coupled to processing system at aproximal portion of the catheter. The system is operable to receive ananalog image signal from the transducer; split the signal into a firstimage signal and a second image signal—the first image signal comprisingsubstantially all of the information of the second image signal—andperform a processing operation on the first image signal and the secondimage signal. The system may further include one or more of a time gaincompensation amplifier operable to produce a TGC amplified first signaland a TGC amplified first signal; an analog-digital-converter; afield-programmable gate array configured to perform the processingoperation; an application-specific integrated processor, a low-band passfilter; and a massively parallel processor array.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an IVUS system according to certain embodiments of theinvention.

FIG. 2 shows a control station for an imaging system.

FIG. 3 shows an control panel of a control station of an imaging system.

FIG. 4 describes components of computer device of certain embodiments.

FIG. 5 provides a schematic of processing circuits.

FIG. 6 is a diagram of ultrasound signal processing in two pathways forimages

FIG. 7 shows a multipath signal processing scheme for ultrasound images.

FIG. 8 shows a signal processing scheme for an image and for aparametric analysis.

FIG. 9 shows a multipath signal processing scheme for flexibility.

DETAILED DESCRIPTION

The invention provides an imaging system that splits incoming image datainto two signals and performs the same processing step on each of thesplit signals.

FIG. 1 shows a diagram of an exemplary IVUS system 101 according tocertain embodiments of the invention. An operator uses control station110 and optional navigational device 125 to operate catheter 112 viapatient interface module (PIM) 105. At a distal tip of catheter 112 isan ultrasonic transducer 114. Computer device 120 works with PIM 105 tocoordinate imaging operations. Imaging operations proceed by rotating animaging mechanism via catheter 112 while transmitting a series ofelectrical impulses to transducer 114 which results in sonic impulsesbeing sent into the patient's tissue. Backscatter from the ultrasonicimpulses is received by transducer 114 and interpreted to provide animage on monitor 103. System 101 is operable for use during diagnosticultrasound imaging of the peripheral and coronary vasculature of thepatient. System 101 can be configured to automatically visualizeboundary features, perform spectral analysis of vascular features,provide qualitative or quantitate blood flow data, or a combinationthereof. Systems for IVUS suitable for use with the invention arediscussed in U.S. Pat. No. 6,673,015; U.S. Pub. 2012/0265077; and U.S.RE40,608 E, the contents of which are incorporated by reference in theirentirety for all purposes.

Operation of system 101 employs a sterile, single use intravascularultrasound imaging catheter 112. Catheter 112 is inserted into thecoronary arteries and vessels of the peripheral vasculature underangiographic guidance. Catheters are described in U.S. Pat. No.7,846,101; U.S. Pat. No. 5,771,895; U.S. Pat. No. 5,651,366; U.S. Pat.No. 5,176,141; U.S. Pub. 2012/0271170; U.S. Pub. 2012/0232400; U.S. Pub.2012/0095340; U.S. Pub. 2009/0043191; U.S. Pub. 2004/0015065, thecontents of which are incorporated by reference herein in their entiretyfor all purposes. System 101 may be integrated into existing and newlyinstalled catheter laboratories (i.e., “cath labs” or “angiographysuites”). The system configuration is flexible in order to fit into theexisting catheter laboratory work flow and environment. For example, thesystem can include industry standard input/output interfaces forhardware such as navigation device 125, which can be a bedside mountedjoystick. System 101 can include interfaces for one or more of an EKGsystem, exam room monitor, bedside rail mounted monitor, ceiling mountedexam room monitor, and server room computer hardware.

System 101 connects to the IVUS catheter 112 via PIM 105, which maycontain a type CF (intended for direct cardiac application)defibrillator proof isolation boundary. All other input/outputinterfaces within the patient environment may utilize both primary andsecondary protective earth connections to limit enclosure leakagecurrents. The primary protective earth connection for controller 125 andcontrol station 110 can be provided through the bedside rail mount. Asecondary connection may be via a safety ground wire directly to thebedside protective earth system. Monitor 103 and an EKG interface canutilize the existing protective earth connections of the monitor and EKGsystem and a secondary protective earth connection from the bedsideprotective earth bus to the main chassis potential equalization post.Monitor 103 may be, for example, a standard SXGA (1280×1024) exam roommonitor. System 101 includes computer device 120 to coordinateoperations.

Computer device 120 generally includes one or more processor coupled toa memory. Any suitable processor can be included such as, for example, ageneral-purpose microprocessor, an application-specific integratedcircuit, a massively parallel processing array, a field-programmablegate array, others, or a combination thereof. In some embodiments,computer 120 can include a high performance dual Xeon based system usingan operating system such as Windows XP professional. Computer 120 may beprovided as a single device (e.g., a desktop, laptop, or rack-mountedunit, or computer 120 may include different machines coupled together(e.g., a Beowulf cluster, a network of servers, a server operating witha local client terminal, other arrangements, or a combination thereof).

Computer device 120 may be configured to perform processing on more thanone image modality (e.g., in parallel). For example, computer 120 mayoperate with real time intravascular ultrasound imaging whilesimultaneously running a tissue classification algorithm referred to asvirtual histology (VH). The application software can include a DICOM3compliant interface, a work list client interface, interfaces forconnection to angiographic systems, or a combination thereof. Computerdevice 120 may be located in a separate control room, the exam room, orin an equipment room and may be coupled to one or more of a customcontrol station, a second control station, a joystick controller, a PS2keyboard with touchpad, a mouse, or any other computer control device.

Computer device 120 may generally include one or more USB or similarinterfaces for connecting peripheral equipment. Available USB devicesfor connection include the custom control stations, optional joystick125, and a color printer. In some embodiments, computer 120 includes oneor more of a USB 2.0 high speed interface, a 10/100/1000 baseT Ethernetnetwork interface, AC power jack, PS2 jack, Potential Equalization Post,1 GigE Ethernet interface, microphone and line jacks, VGA video, DVIvideo interface, PIM interface, ECG interface, other connections, or acombination thereof. As shown in FIG. 1, computer device 120 isgenerally linked to control station 110.

FIG. 2 shows a control system 110 according to certain embodiments.Control station 110 may be provided by any suitable device, such as acomputer terminal (e.g., on a kiosk). In some embodiments, controlsystem 110 is a purpose built device with a custom form factor. A slideout keyboard is located on the bottom for manual text entry. Controlstation 110 may be designed for different installations options. Thestation can be placed directly on a desktop surface. With the optionalbedside mounting kit, control station 110 can be affixed directly to thebedside rail. This mounting kit is slipped over the rail and fixed inplace by tightening two hand screws. Control station 110 can include astandard four hole VESA mount on the underside to allow other mountingconfigurations. Control system 110 may provide a simple-to-use interfacewith frequently-operated functions mapped to unique switches. Controlstation 110 may be powered from, and may communicate with, computer 120using a standard USB 1.1 interface. The system may include a controlpanel 115. In some embodiments, multiple control panels 115 are mountedin both the exam room and/or the control room. A control station for usewith the invention is discussed in U.S. Pat. No. 8,289,284, the contentsof which are incorporated by reference in their entirety for allpurposes.

FIG. 3 shows an control panel 115 of control system 110 according tocertain embodiments. Frequently-operated functions are mapped to contactclosure switches. Those dome switches are covered with a membraneoverlay. The use of dome switches provides a tactile feedback to theoperator upon closure. Control panel 115 may include a pointing devicesuch as a trackball to navigate a pointer on the graphical userinterface of the system.

Control panel 115 may include several screen selection keys. Thesettings key is used to change system settings like date and time andalso permits setting and editing default configurations. The display keymay be used to provide enlarged view for printing. In some embodiments,the print key prints a 6×4 inch photo of the current image on thescreen. Control panel 115 may include a ringdown key that toggles theoperation of ringdown subtraction. A chroma key can turn blood flowoperations on and off. The VH key can operate the virtual histologyengine. A record, stop, play, and save frame key are included for videooperation. Typically, the home key will operate to display the liveimage. A menu key provides access to measurement options such asdiameter, length, and borders. Bookmark can be used while recording aloop to select specific areas of interest. Select (+) and Menu (−) keysare used to make selections.

In some embodiments, the system includes a joystick for navigationaldevice 125. The joystick may be a sealed off-the-shelf USB pointingdevice used to move the cursor on the graphical user interface from thebedside. System 101 may include a control room monitor, e.g., anoff-the-shelf 19″ flat panel monitor with a native pixel resolution of1280×1024 to accept DVI-D, DVI-I and VGA video inputs.

Control station 110 is operably coupled to PIM 115, from which catheter112 extends. Catheter 112 includes an ultrasound transducer 114 locatedat the tip. Any suitable IVUS transducer may be used. For example, insome embodiments, transducer 114 is driven as a synthetic apertureimaging element. Imaging transducer 114 may be approximately 1 mm indiameter and 2.5 mm in length. In certain embodiments, transducer 114includes a piezoelectric component such as, for example, lead zirconiumnitrate or PZT ceramic. The transducer may be provided as an array ofelements (e.g., 64), for example, bonded to a Kapton flexible circuitboard providing one or more integrated circuits. This printed circuitassembly may rolled around a central metal tube, back filled with anacoustic backing material and bonded to the tip of catheter 114. In someembodiments, signals are passed to the system via a plurality of wires(e.g., 7) that run the full length of catheter 112. The wires are bondedto the transducer flex circuit at one end and to a mating connector inPIM 105 at the other. The PIM connector may also contains aconfiguration EPROM. The EPROM may contain the catheter's model andserial numbers and the calibration coefficients which are used by thesystem. The PIM 105 provides the patient electrical isolation, the beamsteering, and the RF amplification. PIM 105 may additionally include alocal microcontroller to monitor the performance of the system and resetthe PIM to a known safe state in the event of loss of communication orsystem failure. PIM 105 may communicate with computer device 120 via alow speed RS232 serial link.

FIG. 4 describes components of computer device 120 according to certainembodiments. Computer device 120 may include a motherboard 129 thatincludes an IVUS signal generation and processing system. FIG. 4provides a high-level diagram and any box shown therein may be taken torepresent a unit of hardware, a unit of functionality to be performed byone or more pieces of hardware, modules of software, or combinationthereof. The signal generation and processing system may include ananalog printed circuit assembly (PCA) 131, an digital PCA 133, one ormore filter modules, and a VH board 135. Analog PCA 131 and digital PCA133 are used to excite transducer 114 via catheter 112 and to receiveand process the gray scale IVUS signals. The VH board 135 is used tocapture and pre-process the IVUS RF signals and transfer them to themain VH processing algorithm as run by a computer processor system(e.g., dual Xeon processors). PIM 105 is directly connected to theanalog PCA 131. A computer system that includes a computer, such as onelike that depicted in FIG. 4, can be configured to perform the signalprocessing of the invention. Exemplary signal processing and systemstherefore are discussed in U.S. Pat. No. 8,298,147; U.S. Pat. No.8,187,191; U.S. Pat. No. 6,450,964; U.S. Pat. No. 5,485,845; U.S. Pub.2012/0220874; U.S. Pub. 2012/0184853; and U.S. Pub. 2007/0232933, thecontents of which are incorporated by reference herein in theirentirety.

FIG. 5 provides a schematic of analog PCA 131 and digital PCA 133according to certain embodiments of the invention. Analog PCA 131 isshown to include amplifier 141, band pass filter 145, mixer 149, lowpass filter 153, and analog-to-digital converter (ADC) 157. Here, theincoming signal is split just after bandpass filtering and prior tomixing by mixer 149. Mixer 149 performs the same function on each of twoor more copies of the same signal. Then, low pass filter 153 performsthe same low pass filtering function on each of the two or more copiesof the same signal. Finally, ADC 157 converts each of the two or morecopies of the same signal into a digital signal, and each of the two ormore copies of the same digital signal is sent to the acquisition FPGA165 for processing. Analog board 131 further includes an interfacemodule 161 for PIM 105, as well as a clock device 169.

The invention provides systems and methods that incorporate the insightthat unexpected benefits can be provided by splitting the signal andperforming the counter-intuitive process of performing the same signalprocessing operations on each copy of the split signal. Establishedthinking suggests splitting a signal to perform different operations oneach copy of the split signal. Here, since computer 120 splits thepathway and performs the same processing operations on each pathway, thesystem is readily adaptable for future changes that would requiredifferent processing operations. In one particular example, a signal isprocessed according to a parametric processing operation that is used tocharacterize the imaged tissue, such as in virtual histology. In someembodiment, virtual histology applications involve a processing stepthat makes use of a neural network comprising interconnecting artificialneurons, e.g., as supplied by a computer processing system. In virtualhistology, a neural network can be taught to characterize tissue and toinfer tissue characteristics from an incoming set of data. In someembodiments, to be effective, a tissue analyzing neural network shouldbe trained on signals that are processed according to the same pathwayas the subject signals upon which the neural network operates. Where theneural network is receiving a signal from, for example, an IVUS systemthat is also being use to provide an image (e.g., on a monitor), andchange in the IVUS processing pathway would diminish the capabilities ofthe neural network. For example, if a physician using IVUS wanted toturn ringdown subtraction on and off, the different signals couldproduce sub-par results in the VH application. In some cases, a newinsight in IVUS imaging may call for an upstream change in signalprocessing. For example, it may be desired to implement a new graphicequalization on IVUS signals using a mixer 149. If a single signal goesthrough mixer 149 and is split thereafter, then implementing the graphicequalization would require re-training the neural network—i.e., theexisting neural network learning would no longer be useful. Where asystem has been deployed with a split upstream of mixer 149, as depictedin FIG. 5, even though mixer 149 may perform the same function on bothpaths when the system is first installed, the system is readily adaptedto the new graphic equalization function when implemented, withoutdisrupting the neural network.

This adaptability becomes particularly useful when the subsequentchanges involve inherently tunable processing parameters such as graphicequalization. One advantage of graphic equalization (or otherparallelized processing such as multiband low pass filtering) is that itallows field-deployed fine tuning. If the signal were not split upstreamof the tunable processor, then the other analysis modality (e.g., VH;high- versus low-frequency IVUS; blood flow characterization; simpledata storage; others; or a combination thereof) would be compromised.While depicted in FIG. 5 as splitting the signal after bandpassfiltering, one insight of the invention is that there can be value insplitting the signal at any point and subsequently performing the sameprocessing step on the split. For example, in some embodiments, a signalis split within a processor such as a field programmable gate array andthe two signal copies are also processed within that processor, with theprocessor performing the same operations on each signal path.

Digital PCA 133 is depicted as having an acquisition FPGA 165, as wellas a focus FPGA 171, and a scan conversion FPGA 179. Focus FPGA 171provides the synthetic aperture signal processing and scan conversion.In some embodiments, a single signal is sent into acquisition FPGA 165;split within FPGA 165; and processed in duplicate within FPGA 165. Insome embodiments, a single signal is sent into acquisition FPGA 171;split within FPGA 171; and processed in duplicate within FPGA 171. Incertain embodiments, two like signals are both focused (e.g., accordingto a synthetic aperture modality) within FPGA 171, having been splitfrom a single incoming signal anywhere upstream from the focusingtransistor hardware of FPGA 171. FPGA 179 provides the final scanconversion of the transducer vector data to Cartesian coordinatessuitable for display via a standard computer graphics card on monitor103. Digital board 133 further optionally includes a safetymicrocontroller 181, operable to shut down PIM 105 as a failsafemechanism. Preferably, digital PCA 133 further includes a PCI interfacechip 175. It will be appreciated that this provides but one exemplaryillustrative embodiment and that one or skill in the art will recognizethat variant and alternative arrangements may perform the functionsdescribed herein. Clock device 169 and acquisition FPGA 165 may operatein synchronization to control the transmission of acquisition sequences.

FIG. 6 provides a diagram of an embodiment of multipath processing ofimage signals. An ultrasound (US) transducer 114 receives (Rx) thesignal that was transmitted (Tx). Further preprocessing operations 131after the ultrasound (US) transmit (Tx) and receive (Rx), can includeany desired bandpass filtering, analog gain, channel matching,demodulation, other steps, or a combination thereof. The analog signalis split into a first image signal and a second image signal and ananalog-digital converter (ADC) performs a processing operation on thefirst image signal and the second image signal. Additional digitalpre-processing operations 137 can include averaging, scaling, and DCoffset correction. It will be appreciated by one skilled in the art thatprocessing operation steps discussed herein can be performed in orderother than shown here. Imaging processing operations 143 can then beperformed and can include scaling, focus, processing, time gaincompensation (TGC), ringdown subtraction, any additional processing, logconversion, other steps, or a combination thereof. Finally, an image canbe prepared by image preparation operations 149 including, for example,any desired processing (e.g., contrast adjustment) and scan conversion.

Image processing operations can include any such operations known in theart or those discussed herein and need not be limited to, nor includeall of, those listed in FIG. 6. In general, a bandpass filter is used toremove or attenuate certain (e.g., non-desired or non-intended)frequencies from the signal. Gain generally refers to adjusting a signalstrength (e.g., with an amplifier) to a desired strength. Demodulationcan include removing a carrier signal from a signal. Averaging can referto average a series of A lines for improved signal-to-noise ratio(sometimes called accumulation). Scaling can refer to a lineartransformation of the signal. DC offset correction can include removingor adding a constant amplitude to a signal to produce an AC signal withan average amplitude near or at zero. Focusing can include usingincoming sounds from adjacent Tx events to improve an A line. Time gaincompensation (TGC) refers to adjusting the signal to compensate for anon-uniform signal strength based on attenuation in the IVUS backscatterstrength relating to an amount of time that the sound signal was passingthrough tissue. Ringdown refers to transient sounds from vibration oftransducer that can be removed in ringdown subtraction. Scan conversioncan include transforming a 3D data set in preparation for a 2D displayand can proceed by a fast Fourier transformation. By scan conversion, aB mode image is prepared from a set of A lines. Signal processing stepsare discussed in more detail in U.S. Pat. No. 8,289,284; U.S. Pat. No.8,187,191; U.S. Pat. No. 6,254,543; U.S. Pat. No. 6,200,268; U.S. Pub.2012/0220874; U.S. Pub. 2011/0087104; and U.S. Pub. 2010/0234736, thecontents of which are incorporated by reference herein in theirentirety.

FIG. 7 shows an alternative embodiment in which a signal is split justafter digitization at the end of preprocessing operations 131. Here, anyof the additional digital pre-processing operations 137, imagingprocessing operations 143, image preparation operations 149, or acombination thereof are performed in duplicate on the first image signaland the second image signal, which contain substantially the sameinformation as one another through at least one of the shared processingsteps.

FIG. 8 depicts an embodiment in which a signal is received andpreprocessing operations 131 are performed, after which the signal issplit, and the first and second copies of the split signal aredigitized. Additional digital pre-processing operations 147 may beperformed on each of the first and second signal. Further, the firstsignal undergoes all of the signal processing discussed above withrespect to FIG. 6. Here, the second signal undergoes processing inpreparation for a parametric analysis such as a VH tissuecharacterization. Any of imaging processing operations 143 may beperformed on the second (VH) signal path, however any or most of themmay not. For example, ringdown subtraction is not performed on the VHpath. Here, final preparation operations 149 for VH characterization caninclude a processing step that involves analysis by a neural network,after which the image can be used to characterize the tissue.

FIG. 9 depicts a multipath signal processing scheme in which a secondsignal path is routed to storage for later flexibility. Here, even wherethe second signal path does not directly contribute to producing ananalytical result simultaneously with the scan converted image providedby the first signal path, the presence of a second signal path shunt insystem 120 allows a later analytical modality to be added to system 120.Any amount of additional digital pre-processing operations 137 may beperformed on the first and second signal path after it is split. Thenthe second signal path can be routed to storage and stored. Storage ofthe second set of signals can have benefit because, even if processingof the first signal path changes over time, the accumulated signalsstored from the second path have all been processed according to thesame steps. A VH algorithm could be introduced and the neural networkcould be trained on the stored data. A subsequent problem in the firstpath could be diagnosed by calibrating first path images against pathtwo data to establish, at what point in time, some change had occurred.

As used herein, the word “or” means “and or or”, sometimes seen orreferred to as “and/or”, unless indicated otherwise.

INCORPORATION BY REFERENCE

References and citations to other documents, such as patents, patentapplications, patent publications, journals, books, papers, webcontents, have been made throughout this disclosure. All such documentsare hereby incorporated herein by reference in their entirety for allpurposes.

Equivalents

Various modifications of the invention and many further embodimentsthereof, in addition to those shown and described herein, will becomeapparent to those skilled in the art from the full contents of thisdocument, including references to the scientific and patent literaturecited herein. The subject matter herein contains important information,exemplification and guidance that can be adapted to the practice of thisinvention in its various embodiments and equivalents thereof.

What is claimed is:
 1. A method of imaging tissue, the methodcomprising: receiving an analog image signal from an ultrasonictransducer; transmitting the received signal to a processing systemcoupled to the transducer; splitting the signal to produce a first imagesignal and a second image signal, the first image signal comprisingsubstantially all of the information of the second image signal; andperforming a processing operation on the first image signal and thesecond image signal.
 2. The method of claim 1, wherein the processingoperation comprises time gain compensation amplification, and the methodfurther comprises converting the TGC amplified first signal into adigital signal and converting the TGC amplified second signal into adigital signal, wherein the digitized first signal is substantially thesame as the digitized second signal.
 3. The method of claim 1, furthercomprising converting the analog signal to a digital signal prior to thesplitting step.
 4. The method of claim 3, wherein the processingoperation is performed within a field programmable gate array and theprocessed first image signal is substantially the same as the processedsecond image signal.
 5. The method of claim 1, wherein the processingoperation is performed using one selected from the list consisting of afield-programmable gate array, an application-specific integratedprocessor, a time-gain compensation amplifier, a low-band pass filter,and a massively parallel processor array.
 6. The method of claim 1,further comprising: deriving a first type of image from the first imagesignal; and deriving a second type of signal from the second type ofsignal.
 7. The method of claim 6, wherein the first type of imagecomprises a grayscale image and the second type of signal comprises atissue characterization.
 8. The method of claim 1, further comprisingusing one or more analog-to-digital converter to digitize the firstimage signal and the second image signal.
 9. The method of claim 1,further comprising an additional processing step on the first imagesignal and a second processing step on the second image signal.
 10. Anintravascular ultrasound imaging system, the system comprising: anelongated catheter comprising a transducer at a distal portion of thecatheter and coupled to processing system at a proximal portion of thecatheter and operable to: receive an analog image signal from thetransducer; split the signal into a first image signal and a secondimage signal, the first image signal comprising substantially all of theinformation of the second image signal; and perform a processingoperation on the first image signal and the second image signal.
 11. Thesystem of claim 10, wherein the processing system comprises: a time gaincompensation amplifier operable to produce a TGC amplified first signaland a TGC amplified first signal; and an analog-digital-converteroperable to convert the TGC amplified first signal into a digital signaland converting the TGC amplified second signal into a digital signal,wherein the digitized first signal is substantially the same as thedigitized second signal.
 12. The system of claim 10, further comprisingan analog-digital-converter configured to convert the analog imagesignal to a digital signal prior to the splitting step.
 13. The systemof claim 12, further comprising a field-programmable gate arrayconfigured to perform the processing operation to produce a processedfirst image signal and a processed second image signal, wherein theprocessed first image signal is substantially the same as the processedsecond image signal.
 14. The system of claim 10, further comprising oneselected from the list consisting of a field-programmable gate array, anapplication-specific integrated processor, a time-gain compensationamplifier, a low-band pass filter, and a massively parallel processorarray.
 15. The system of claim 10, further wherein the processing systemis operable to derive a first type of image from the first image signaland to derive a second type of signal from the second type of signal.16. The system of claim 15, wherein the first type of image comprises agrayscale image and the second type of signal comprises a tissuecharacterization.
 17. The system of claim 10, further comprising one ormore analog-to-digital converter configured to digitize the first imagesignal and the second image signal.
 18. The system of claim 15, whereinthe first type of image is a B-mode image and the second type of imageis a virtual histology image.